The basic steps for processing light-sensitive materials are generally color development and de-silvering. In the color developing step, exposed silver halide is reduced by the action of a color developing agent, thereby forming silver, while at the same time the oxidized color developing agent reacts with a coupler, thereby providing a dye image. In the subsequent de-silvering step, the silver formed during the color developing step is oxidized by the action of an oxidizing agent (generally called a "bleaching agent"), and thereafter dissolved by a silver ion-complexing agent generally called a "fixing agent". After the de-silvering step, the dye image alone is present in the light-sensitive material.
The de-silvering process can be carried out in two manners. One is to use two baths, i.e., a bleaching bath containing a bleaching agent, and a fixing bath containing a fixing agent. The other is to carry out the de-silvering using a single bath, i.e., a bleach-fixing bath containing both the bleaching agent and fixing agent.
In practice, the photographic processing includes, as well as the above basic steps, various auxiliary steps for the purpose of, for example, providing desirable photographic and physical properties, or improving the storage stability of the images. Typical examples include a hardening bath, a stopping bath, an image-stabilizing bath, and a washing bath.
In general, as bleaching agents, red prussiate, dichromic acid salts, ferric chloride, aminopolycarboxylic acid/iron (III) salts, and persulfuric acid salts are known.
These compounds, however, have some disadvantages. Red prussiate and dichromic acid salts tend to cause pollution problems, because they contain cyan and hexavalent chromium. Therefore, the use of such compounds requires special equipment for the treatment thereof. Ferric chloride produces iron hydroxide in the subsequent washing step and causes the formation of stain; therefore, it is not totally satisfactory. Persulfuric acid salts are very poor in the bleaching action and thus have a disadvantage in that a considerably long period of time is required for the bleaching step. In order to improve this poor bleaching activity, it has been proposed to use a bleach-accelerating agent in combination. However, the persulfuric acid salts themselves are defined as "dangeous material" according to the Fire Fighting Regulations and is required to apply various treatments for the storage thereof. Thus they are not totally satisfactory.
Aminopolycarboxylic acid/iron (III) complex salts (particularly an ethylenediaminetetraacetic acid/iron (III) complex salt) are now most widely used as bleaching agents, because they cause less pollution problems and are free from the problem of poor storage stability as is encountered in the case of persulfuric acid salts. These complex salts, however, are not always sufficiently satisfactory in bleaching power. Thus, only in the case that they are used in bleaching or bleach-fixing of a low sensitivity silver halide color material using mainly a silver chlorobromide emulsion, can the desired object be completely satisfactorily attained. In processing, however, a high sensitivity light-sensitive material which uses mainly a silver chlorobromoiodide or silver iodobromide emulsion and is color sensitized, particularly a color reversal light-sensitive material for cameras, using a high silver content emulsion, and a color negative light-sensitive material for cameras, these complex salts have disadvantages in that de-silvering is achieved only insufficiently, and a long period of time is needed for bleaching.
To accelerate the de-silvering process, West German Pat. No. 866,605 discloses a bleach-fixing solution containing a aminopolycarboxylic acid/iron (III) complex salt and a thiosulfuric acid salt. If, however, an aminopolycarboxylic acid/iron (III) complex salt having originally poor oxidizing power (bleaching power) is used in combination with the thiosulfuric acid salt having a reducing power, the bleaching power of the aminopolycarboxylic acid salt is seriously decreased. As a result, a light-sensitive material of high sensitivity and high silver content is quite difficult to de-silver sufficiently. Thus the above bleach-fixing solution is not totally satisfactory.
In order to increase the bleaching power of the aminopolycarboxylic acid/iron (III) complex salt, a method of adding various bleach-accelerating agents to a bleaching bath, or a bleach-fixing bath, or their prebaths has been proposed. Typical examples of such bleach-accelerating agents are mercapto compounds as described in U.S. Pat. No. 3,893,858, British Pat. No. 138,842, and Japanese Patent Application (OPI) No. 141623/78 (the term "OPI" as used herein means a "published unexamined Japanese patent application"), compounds containing a disulfide bond as described in Japanese Patent Application (OPI) No. 95630/78, thiazolidine derivatives as described in Japanese Patent Publication No. 9854/78, isothiourea derivatives as described in Japanese Patent Application (OPI) No. 94927/78, thiourea derivatives as described in Japanese Patent Publication Nos. 8506/70 and 26586/74, thioamide compounds as described in Japanese Patent Application (OPI) No. 42349/74, and dithiocarbamic acid salts as described in Japanese Patent Application (OPI) No. 26506/80.
Even by using a bleach-fixing solution with the above bleach-fixing agent added thereto, a sufficient bleaching effect is difficult to obtain, depending on the specific type of the light-sensitive material.
As described above, many problems are encountered in sufficiently bleaching a color-sensitized light-sensitive material. It is also known that in the case in which bleach-fixing is carried out continuously, when the amount of a component accumulated in the bleach-fixing solution, particularly iodide ion released from the light-sensitive material, exceeds a critical level, the bleaching speed is seriously decreased. The amount of the iodide ion accumulated in the bleach-fixing solution greatly depends on the halogen composition of a silver halide emulsion used in the light-sensitive material, or on a critical accumulation amount calculated from the amount of the bleach-fixing solution being replenished. It has now been specifically found that when the amount of the iodide ion exceeds 1.2.times.10.sup.-3 gram ion per liter of the bleach-fixing solution, the bleaching speed is influenced.
It is known that a sensitizing dye adsorbed on silver halide is strongly adsorbed on developed silver during the developing process, thereby decreasing the bleaching speed. That is, Matsuo et al, Nippon Shashin Gakkaishi (Journal of Japanese Photographic Association), Vol. 39 (2), p. 81 (1976) describes that the physical properties of the sensitizing dye, particularly adsorption properties and the charged state, exert influences on the bleaching speed.
If, however, the amount of iodide ion accumulated in the bleach-fixing solution is greatly increased, the bleaching speed cannot be improved simply by taking into consideration only the physical properties of the sensitizing agent as described in the above Matsuo et al reference.